As someone who went through COVID hell I can tell you that the vaccine might not work for everyone. I was fully vaccinated (2 shots at the time) and I still got it, in the words of the doctor at the hospital, "Worse than anyone I've seen that's been vaccinated." 2 weeks in the hospital.
I got them because I felt it was the right thing to do. But i can't help but think it was a mistake. Even after I went through hell my mindset didn't change. Personal choice. So i have no issue with any athlete or anyone choosing not to be vaccinated.